Resistive random-access memories (RRAMs) have generated significant interest recently as a potential candidate for ultra-high density non-volatile information storage. A typical RRAM device consists of an insulator layer sandwiched between a pair of electrodes and exhibits electrical pulse induced hysteretic resistance switching effects. The resistance switching has been explained by the formation of conductive filaments inside the insulator due to Joule heating and electrochemical processes in binary oxides (e.g. NiO and TiO2) or redox processes for ionic conductors including oxides, chalcogenides and polymers. Resistance switching has also been explained by field-assisted diffusion of ions in TiO2 and amorphous silicon (a-Si) films.
In the case of a-Si structures, voltage-induced diffusion of metal ions into the silicon leads to the formation of conductive filaments that reduce the resistance of the a-Si structure. These filaments remain after the biasing voltage is removed, thereby giving the device its non-volatile characteristic, and they can be removed by reverse diffusion of the ions back to the metal electrode under the motive force of a reverse polarity applied voltage.
Resistive devices formed by an a-Si structure sandwiched between two metal electrodes have been shown to exhibit this controllable resistive characteristic. However, such devices typically have micron sized filaments which may prevent them from being scaled down to the sub-100 nanometer range. Such devices may also require high forming voltages that can lead to device damage and can limit production yields.